"I think it's very important people understand that re-education through labour is a system that is under the control of administrative or police authorities in China, not the judicial system.

"All of the people who are incarcerated in this system have wound up there without the benefit of a defence counsel, without access to the evidence that's presented against them and without a decision being rendered about the sentence by a judge. So it is a profoundly arbitrary system of detention."

Most of those sentenced to the camps are accused of prostitution, drug addiction or petty criminal offences, although no criminal conviction is necessary.

The system has faced growing criticism for being open to abuse and public anger has erupted in recent months over sentences deemed too harsh.